焦炉的吸气管应用5×103Pa（510mmH2O）做泄压试验，20min压力降不超过（）%为合格。
A、5
B、10
C、15
D、20
参考答案：B
点P（3，4，5）关于原点的对称点是______．
Tom wanted to play football with his friends in the street，but his father told him ______．
A．not to
B．not to do
C．not do it
D．do not to
